/*
 * Copyright (c) 1997, 2003, Oracle and/or its affiliates. All rights reserved.
 * ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
 *
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 *
 *
 *
 */

package java.awt.geom;

import java.util.*;

/**
 * A utility class to iterate over the path segments of an arc
 * through the PathIterator interface.
 *
 * @author Jim Graham
 */
class ArcIterator implements PathIterator {

  double x, y, w, h, angStRad, increment, cv;
  AffineTransform affine;
  int index;
  int arcSegs;
  int lineSegs;

  ArcIterator(Arc2D a, AffineTransform at) {
    this.w = a.getWidth() / 2;
    this.h = a.getHeight() / 2;
    this.x = a.getX() + w;
    this.y = a.getY() + h;
    this.angStRad = -Math.toRadians(a.getAngleStart());
    this.affine = at;
    double ext = -a.getAngleExtent();
    if (ext >= 360.0 || ext <= -360) {
      arcSegs = 4;
      this.increment = Math.PI / 2;
      // btan(Math.PI / 2);
      this.cv = 0.5522847498307933;
      if (ext < 0) {
        increment = -increment;
        cv = -cv;
      }
    } else {
      arcSegs = (int) Math.ceil(Math.abs(ext) / 90.0);
      this.increment = Math.toRadians(ext / arcSegs);
      this.cv = btan(increment);
      if (cv == 0) {
        arcSegs = 0;
      }
    }
    switch (a.getArcType()) {
      case Arc2D.OPEN:
        lineSegs = 0;
        break;
      case Arc2D.CHORD:
        lineSegs = 1;
        break;
      case Arc2D.PIE:
        lineSegs = 2;
        break;
    }
    if (w < 0 || h < 0) {
      arcSegs = lineSegs = -1;
    }
  }

  /**
   * Return the winding rule for determining the insideness of the
   * path.
   *
   * @see #WIND_EVEN_ODD
   * @see #WIND_NON_ZERO
   */
  public int getWindingRule() {
    return WIND_NON_ZERO;
  }

  /**
   * Tests if there are more points to read.
   *
   * @return true if there are more points to read
   */
  public boolean isDone() {
    return index > arcSegs + lineSegs;
  }

  /**
   * Moves the iterator to the next segment of the path forwards
   * along the primary direction of traversal as long as there are
   * more points in that direction.
   */
  public void next() {
    index++;
  }

  /*
   * btan computes the length (k) of the control segments at
   * the beginning and end of a cubic bezier that approximates
   * a segment of an arc with extent less than or equal to
   * 90 degrees.  This length (k) will be used to generate the
   * 2 bezier control points for such a segment.
   *
   *   Assumptions:
   *     a) arc is centered on 0,0 with radius of 1.0
   *     b) arc extent is less than 90 degrees
   *     c) control points should preserve tangent
   *     d) control segments should have equal length
   *
   *   Initial data:
   *     start angle: ang1
   *     end angle:   ang2 = ang1 + extent
   *     start point: P1 = (x1, y1) = (cos(ang1), sin(ang1))
   *     end point:   P4 = (x4, y4) = (cos(ang2), sin(ang2))
   *
   *   Control points:
   *     P2 = (x2, y2)
   *     | x2 = x1 - k * sin(ang1) = cos(ang1) - k * sin(ang1)
   *     | y2 = y1 + k * cos(ang1) = sin(ang1) + k * cos(ang1)
   *
   *     P3 = (x3, y3)
   *     | x3 = x4 + k * sin(ang2) = cos(ang2) + k * sin(ang2)
   *     | y3 = y4 - k * cos(ang2) = sin(ang2) - k * cos(ang2)
   *
   * The formula for this length (k) can be found using the
   * following derivations:
   *
   *   Midpoints:
   *     a) bezier (t = 1/2)
   *        bPm = P1 * (1-t)^3 +
   *              3 * P2 * t * (1-t)^2 +
   *              3 * P3 * t^2 * (1-t) +
   *              P4 * t^3 =
   *            = (P1 + 3P2 + 3P3 + P4)/8
   *
   *     b) arc
   *        aPm = (cos((ang1 + ang2)/2), sin((ang1 + ang2)/2))
   *
   *   Let angb = (ang2 - ang1)/2; angb is half of the angle
   *   between ang1 and ang2.
   *
   *   Solve the equation bPm == aPm
   *
   *     a) For xm coord:
   *        x1 + 3*x2 + 3*x3 + x4 = 8*cos((ang1 + ang2)/2)
   *
   *        cos(ang1) + 3*cos(ang1) - 3*k*sin(ang1) +
   *        3*cos(ang2) + 3*k*sin(ang2) + cos(ang2) =
   *        = 8*cos((ang1 + ang2)/2)
   *
   *        4*cos(ang1) + 4*cos(ang2) + 3*k*(sin(ang2) - sin(ang1)) =
   *        = 8*cos((ang1 + ang2)/2)
   *
   *        8*cos((ang1 + ang2)/2)*cos((ang2 - ang1)/2) +
   *        6*k*sin((ang2 - ang1)/2)*cos((ang1 + ang2)/2) =
   *        = 8*cos((ang1 + ang2)/2)
   *
   *        4*cos(angb) + 3*k*sin(angb) = 4
   *
   *        k = 4 / 3 * (1 - cos(angb)) / sin(angb)
   *
   *     b) For ym coord we derive the same formula.
   *
   * Since this formula can generate "NaN" values for small
   * angles, we will derive a safer form that does not involve
   * dividing by very small values:
   *     (1 - cos(angb)) / sin(angb) =
   *     = (1 - cos(angb))*(1 + cos(angb)) / sin(angb)*(1 + cos(angb)) =
   *     = (1 - cos(angb)^2) / sin(angb)*(1 + cos(angb)) =
   *     = sin(angb)^2 / sin(angb)*(1 + cos(angb)) =
   *     = sin(angb) / (1 + cos(angb))
   *
   */
  private static double btan(double increment) {
    increment /= 2.0;
    return 4.0 / 3.0 * Math.sin(increment) / (1.0 + Math.cos(increment));
  }

  /**
   * Returns the coordinates and type of the current path segment in
   * the iteration.
   * The return value is the path segment type:
   * SEG_MOVETO, SEG_LINETO, SEG_QUADTO, SEG_CUBICTO, or SEG_CLOSE.
   * A float array of length 6 must be passed in and may be used to
   * store the coordinates of the point(s).
   * Each point is stored as a pair of float x,y coordinates.
   * SEG_MOVETO and SEG_LINETO types will return one point,
   * SEG_QUADTO will return two points,
   * SEG_CUBICTO will return 3 points
   * and SEG_CLOSE will not return any points.
   *
   * @see #SEG_MOVETO
   * @see #SEG_LINETO
   * @see #SEG_QUADTO
   * @see #SEG_CUBICTO
   * @see #SEG_CLOSE
   */
  public int currentSegment(float[] coords) {
    if (isDone()) {
      throw new NoSuchElementException("arc iterator out of bounds");
    }
    double angle = angStRad;
    if (index == 0) {
      coords[0] = (float) (x + Math.cos(angle) * w);
      coords[1] = (float) (y + Math.sin(angle) * h);
      if (affine != null) {
        affine.transform(coords, 0, coords, 0, 1);
      }
      return SEG_MOVETO;
    }
    if (index > arcSegs) {
      if (index == arcSegs + lineSegs) {
        return SEG_CLOSE;
      }
      coords[0] = (float) x;
      coords[1] = (float) y;
      if (affine != null) {
        affine.transform(coords, 0, coords, 0, 1);
      }
      return SEG_LINETO;
    }
    angle += increment * (index - 1);
    double relx = Math.cos(angle);
    double rely = Math.sin(angle);
    coords[0] = (float) (x + (relx - cv * rely) * w);
    coords[1] = (float) (y + (rely + cv * relx) * h);
    angle += increment;
    relx = Math.cos(angle);
    rely = Math.sin(angle);
    coords[2] = (float) (x + (relx + cv * rely) * w);
    coords[3] = (float) (y + (rely - cv * relx) * h);
    coords[4] = (float) (x + relx * w);
    coords[5] = (float) (y + rely * h);
    if (affine != null) {
      affine.transform(coords, 0, coords, 0, 3);
    }
    return SEG_CUBICTO;
  }

  /**
   * Returns the coordinates and type of the current path segment in
   * the iteration.
   * The return value is the path segment type:
   * SEG_MOVETO, SEG_LINETO, SEG_QUADTO, SEG_CUBICTO, or SEG_CLOSE.
   * A double array of length 6 must be passed in and may be used to
   * store the coordinates of the point(s).
   * Each point is stored as a pair of double x,y coordinates.
   * SEG_MOVETO and SEG_LINETO types will return one point,
   * SEG_QUADTO will return two points,
   * SEG_CUBICTO will return 3 points
   * and SEG_CLOSE will not return any points.
   *
   * @see #SEG_MOVETO
   * @see #SEG_LINETO
   * @see #SEG_QUADTO
   * @see #SEG_CUBICTO
   * @see #SEG_CLOSE
   */
  public int currentSegment(double[] coords) {
    if (isDone()) {
      throw new NoSuchElementException("arc iterator out of bounds");
    }
    double angle = angStRad;
    if (index == 0) {
      coords[0] = x + Math.cos(angle) * w;
      coords[1] = y + Math.sin(angle) * h;
      if (affine != null) {
        affine.transform(coords, 0, coords, 0, 1);
      }
      return SEG_MOVETO;
    }
    if (index > arcSegs) {
      if (index == arcSegs + lineSegs) {
        return SEG_CLOSE;
      }
      coords[0] = x;
      coords[1] = y;
      if (affine != null) {
        affine.transform(coords, 0, coords, 0, 1);
      }
      return SEG_LINETO;
    }
    angle += increment * (index - 1);
    double relx = Math.cos(angle);
    double rely = Math.sin(angle);
    coords[0] = x + (relx - cv * rely) * w;
    coords[1] = y + (rely + cv * relx) * h;
    angle += increment;
    relx = Math.cos(angle);
    rely = Math.sin(angle);
    coords[2] = x + (relx + cv * rely) * w;
    coords[3] = y + (rely - cv * relx) * h;
    coords[4] = x + relx * w;
    coords[5] = y + rely * h;
    if (affine != null) {
      affine.transform(coords, 0, coords, 0, 3);
    }
    return SEG_CUBICTO;
  }
}
